After I changed wheels and tires (Titan7 T-S5 20" staggered combo w/Michelin A/S3+) and chatting with others who have done something similar (such as 19" or 18" square and same width as OEM), the biggest difference when it comes to efficiency at high-speeds (if using the same width tires - regardless of make/model of tire), is the rim face design. Going with a fairly open design will generally cause much more turbulence and the penalty for efficiency increases exponentially, the faster you drive. In my case, I pay double penalty - having wider rear tires, greater rear offset, and a more open rim design...so at 80mph, I am burning over 480wh/mi consistently vs. 380wh/mi on the factory setup.